Gearing arrangement for rotary and reciprocable hammer drill



July 21, 1970 P. SCHMUCK 3,521,49?

GEARING ARRANGEMENT FOR ROTARY AND RECIPROCABLIL'. HAMMER DRILL FiledJuly D, 19GB United States Patent Office 3,521,497 Patented July 21,1970 3,521,497 GEARING ARRANGEMENT FOR ROTARY AND RECIPROCABLE HAMMERDRILL Peter Schmuck, Mauren, Liechtenstein, assignor to HiltiAktiengesellschaft, Schaan Furstentum, Liechtenstein Filed July 9, 1968,Ser. No. 743,374 Claims priority, application Germany, July 24, 1967,

H 59,672 Int. Cl. F16h 25/12; B2Sd 9/00 U.S. Cl. 74-22 1 Claim ABSTRACTF THE DISCLOSURE BACKGROUND OF THE INVENTION In known hammer drills,wherein the drill is both rotated and axially reciprocated by a drivingmotor, preferably an electric motor, the output torque of the drivingmotor is divided into two work functions, one effective to rotate thedrill and the other effective to reciprocate the drill along the drillaxis. The drive movement is transmitted from the motor driving shaft,which carries a driving pinion, to a single first gear engaging thedriving pinion. The axial reciprocation of the drill is effected by thissingle gear and, through another gear or another gear train engaging thefirst gear, the drill is rotated. In these arrangements, both partialforces or partial torques must be transmitted by only that single toothof the driving pinion which happens to be in engagement with the lirstor output gear.

To attain good drilling eiciency, a relatively larg driving power ortorque must be applied in these hammer drills, while the weight and thevolume of the drills, and thus of the driving motor, must be kept assmall as possible. For this reason, the drive shaft of the motor mustrotate at very high angular velocities. However, due to the fact thatthe angular velocity of the drill and the beating frequency of thehammer effective to reciprocate the drill axially, must be smaller, bymultiple, than the r.p.m. of the motor drive shaft, a large gearreduction ratio of the transmission is necessary. To attain this largegear reduction ratio with the fewest possible gears, the motor drivingpinion must be as small as possible or must have the fewest possibleteeth. This results in an undercut tooth form which is very unfavorablewith respect to bending strength.

During operation of such a hammer drill, the gears, and especially thedriving pinion, are under such a heavy strain, due to the beating of thehammer and, for example, by sudden jamming of the drill, that, as aresult of this unfavorable tooth form of the driving pinion, toothbreakages at the driving pinion occur and, as a consequence, toothbreakages occur, at least in part, in other gears of the gear reducingarrangement.

SUMMARY OF THE INVENTION This invention relates to hammer drills of thetype in which the drill is both rotated and axially reciprocated and,more particularly, to an improved gearing arrangement for such a hammerdrill and which avoids the disadvantages of prior arrangements.

In accordance with the invention, this objective is obtained by dividingthe power required for the drives of the two work functions into twopartial forces or torques immediately at the driving pinion of themotor. These two partial forces or torques are then directed into twodifferent force or torque paths by two gears directly engaging thedriving pinion of the motor and each included in a respective differentone of the two drives. With this arrangement, only one of the twopartial torques or forces must be transmitted by the then engaged toothof the driving pinion, whereby the strain on the teeth of the drivingpinion is greatly reduced.

Advantageously, the two gears directly engaging the motor driving pinionare arranged exactly or approximately diametrically opposite each other.Thereby, the bending moments acting on the shaft of the driving pinionthrough the teeth of the latter are, for the most part, equalized. Anadditional safety factor .against tooth breakage is thereby obtained.

An object of the present invention is to provide an improved gearingarrangement for a hammer drill of the type including two drives, onerotating the drill and other axially reciprocating the drill.

Another object of the invention is to provide such a gearing arrangementin which the two partial torques are provided directly at, orimmediately at, the driving pinion of a motor driving the drill.

A further object of the invention is to provide such a gearingarrangement in which each of the two drives includes a respective gear,and these two gears are directly engaged with the driving pinion.

Still another object of the invention is to provide such a gearingarrangement in which the two gears directly or immediately engaged withthe driving pinion are arranged substantially diametrically oppositeeach other.

A further object of the invention is to provide such a gearingarrangement in which the strain on the teeth of the motor driving pinionis greatly reduced.

A further object of the invention is to provide such a gearingarrangement in which bending moments, acting on the shaft of the drivingpinion through the teeth of the latter, are substantially equalized.

Another object of the invention is toprovide such a gearing arrangementproviding a greatly increased safety factor against breakage ofgearteeth.

For an understanding of the principles of the invention, reference ismade to the following description of a typical embodiment thereof asillustrated in the acompanyng drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, the single figure is anelevation view, partly in section, illustrating an exemplary embodimentof a hammer drill incorporating the gearing arrangement of the presentinvention.

DESCRIPTION 0F THE PREFERRED EMBODIMENT The hammer drill illustrated,solely by way of example, in the drawing includes a casing 1 to which issecured an electric motor 2 for driving the drill. Motor 2 includes anantifriction bearing 3 rotatably supporting its output or driving shaft4 t0 which is secured a driving or output pinion 5. Pinion 5 meshesdirectly with two gears, a gear 6 and a gear 7.

Gear 6 is secured to rotate with a shaft 10= rotatably mounted inaxially spaced antifriction bearings 8 and 9. Shaft 10 has secured torotate therewith a conical or bevel pinion 11 which meshes with a bevelgear 13, the bevel pinion 11 being integral with or fxedly secured tothe upper end of shaft 10. Bevel pinion 13 is fixed to a cylinder orcylindrical sleeve 12 which is rotatably supported by an antifrictionbearing 14. Bevel gear 13 thus transmits the rotation of bevel pinion11, gear 6 and driving pinion to sleeve 12.

1 Sleeve 12 has an outer end 15 in which is non-'rotationally secured atool holder 16 which is rotatably supported in an antifriction bearing18 mounted in a sleeve 17 secured to casing 1 of the hammer drill.

vTool holder 16 has a bore extending completely axially therethroughlfor longitudinal guiding and rotational entrainment of the drillingtool 19. For this purpose, the bore and the drill are formed with matingpolygonal cross sections, such as hexagonal cross sections, for example.The mating shank of drill or drilling tool 19 is axially displaceable intool holder 16, and the end 19a of tool 19 extends into the bore 12a ofcylinder or cylindrical sleeve 12. A pivoted holding strap 20 isprovided to restrain tool 19 from falling out of the tool holder, andlthis strap can be pivoted out of the way for changing the tool 19.

VWhen the hammer drill is in operation, a hammer 21, designed as apneumatic piston, beats on the inner end 19a of drill 19, the hammer 21being axially reciprocable in the cylinder or cylindrical sleeve 12.Hammer 21 is operated, through the medium of an air cushion 22, by adrive piston 23 axially reciprocated in cylinder bore 12a. Through themedium of piston 23 and air cushion 22, axial reciprocation is impartedto hammer 21 in a known manner, and the kinetic energy of hammer 21 istransmitted, as a sudden impact, to drill 19 as hammer 21 strikes theinner end 19a of the shank of tool 19.

Drive piston 23 is reciprocated by means of a connecting rod 26 whichhas one end pivotally connected to piston 23 by means of a pin or bolt24- extending diametrically of piston 23. The other end of connectingrod 26 is articulated on a crank pin 25a of a chank shaft 25 rotatablysupported in bearings 27 and 28. Gear 7, meshing directly with drivingpinion 5, is ixedly secured to crank shaft 25.

In the usual manner, a switch 30 is mounted in handle 29 of the hammerdrill for the purpose of starting and stopping the hammer drill.

What is claimed is:

-1. In a hammer drill of the type driven by a motor having: a drivingpinion, and including two drives, one rotating the drill and the otherreciprocating the drill along the drill axis, a gearing arrangementcomprising, in combination, two gears each meshing directly with saiddriving pinion and each included in a respective different one of saiddrives; one of said drives including crank means directly driven by oneof said two gears; the other of said drives including a rotatable sleeveand reduction gearing means connecting the other of said two gears tosaid r0- tatable sleeve.

References Cited UNITED STATES PATENTS 3,161,241 12/1964 Allen et al74-22 WESLEY S. RAT LIFF, JR., Primary Examiner U.S. Cl. X.R.

